Currently, it's `'bitmex', 'binance', 'bithumb', 'bitfinex', 'okex', 'huobipro', 'bittrex', 'poloniex', 'kucoin', 'cryptopia'` (planned to include top 20, just fixed the message on home page)
The general idea is awesome. Excited about ranking using the bitcoinity metric mentioned by the top comment.